How the Ancient City Sewer System Handles Record Rain

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More than 8 inches of rain fell on parts of New York City in the span of one day this week, flooding parts of Queens and Staten Island and submerging subway tracks under water. But the city's ancient pipes and sewer systems were able to withstand the deluge and properly divert the steady rain in most cases.

"Most of the areas have cleared out, the roadways have been cleared by Department of Environmental Protection, drains have been cleared up,” said Joesph Bruno, commissioner of the New York City Office of Emergency Management, Monday afternoon.

More than 1,100 New Yorkers called 311 to report backed up sewers and flooded streets during the rain, according to the DEP. The number is high, but isn't close to the 1,800 calls made in April 2007 when a storm dumped 7 inches of rain in northnern Manhattan, breaking the previous record set in 1882, Sklerov said.

Since 2002, the city has spent $2 billion on upgrading and maintaining an aging sewer system, which dates to the 1930s — and even the 1870s in some places.

The DEP said $380 million has been spent in Staten Island and $242 million in southeast Queens to install high level storm systems and sewer lines, and to implement programs, like Bluebelt on Staten Island, which directs storm water to natural wetlands.

"Eventually all of that water build up does leave," said Rae Zimmerman, a professor of planning and public administration at New York University. "There were certain pockets within the city that were very badly hit, and always are, even in less rain, but for the most part you have a lot of the rain water buildup being released."

Zimmerman said despite the vast amount of concrete in the city, the so-called elevated grates — the newer sewer grates built into the sidewalk — help prevent much of the water from directly entering the city’s subway tunnels.

There are also elevated grates — like on the medians on Broadway on the Upper West Side — where concrete walls  about 6 to 8 inches tall, allow rain water to flow in, while blocking debris from clogging the drains. The more water that enters the sewers that way, the less likely it is to flood the subway tunnels.

With heavy rains expected, the city’s Department of Environmental Protection last Saturday sent crews to clean flood prone areas and inspect the catch basins where debris can block the flow of water, according to department spokesman Farrell Sklerov.

There were 21 sewer maintenance crews on the streets as heavy rain fell Sunday. On a regular day, the DEP has about three crews on duty for the city. On Monday, there were 32 crews dispersed around the city responding to complaints.

Although Staten Island saw heavy flooding, as well as Sunset Park and East Queens, Sklerov said the unique land leaves the DEP with few options for preventing future floods. 

“A lot of those areas, typically, have the highest incidence of flooding due to the topography of the area; they are low laying areas where water tends to flow to the lowest point, so it tends to pool in certain areas,” he said.

Zimmerman, the professor, said that in addition to replacing aging pipes, the city needs to add "more absorptive natural vegetation."

"I think we’re going to have to look at where our infrastructure and development is located relative to waterways and areas that are prone to flooding," she said.

She suggested that residents of coastal city's may have to consider moving inland, in the near future.

Additional reporting by Kate McGee